The use of bone graft substitutes for treatment of bone injuries/illnesses is continuously expanding with an increasingly active and aging population. Among the clinical indications that bone graft substitutes are being used for are bone fractures, bone cysts, prosthetic joint revision procedures involving bone loss, avascular necrosis of the femoral head, spinal fusions due to degenerative disc disease, oral maxillofacial bone defects and reconstructions, and osteoporotic fractures. All these clinical indications may cause limited mobility and often, particularly in the elderly, can, in extreme cases, result in death. These clinical indications often require surgical bone grafting to prevent delayed or non-unions from occurring. Revision surgery should be avoided if possible because bone healing rates are typically lower after a delayed or non-union has developed. Therefore, effective bone graft substitutes are an important treatment option for repair of bone defects and fractures.
The major problem associated with bone regeneration is the lack of a suitable scaffolding materials which can retain its shape and stay within the bone defect during the healing process but which is also compatible with the body. Properties which the bone regeneration material should possess include biocompatibility, porosity, strength, cohesiveness, shape retention, durability, and elasticity, in order to facilitate consistent regeneration of bone in the desired location, amount, and volume. Therefore, such material must have approximately the same porosity and structure of normal bone, but must not be susceptible to over hydration and diffusion from the surgical site.
Current research is focused around the development of bone graft substances that can be easily packed into irregular bone defects and once implanted in place stay in a cohesive mass. The graft substance has an inherent cohesive consistency preventing it from becoming diluted with bodily fluids, such as blood, and losing its original implanted shape.
The use of carrier matrices to promote the formation of bone at a site in a patient is well known, and related products are currently available on the market, such as Mastergraft® Putty, by Medtronic Sofamor Danek (Memphis, Tenn.). These matrices are typically in the form of a relatively large, soft collagen sponge or dry cake. Before insertion into the target site, the sponge is wetted, usually with sterile water or bone marrow aspirated from the patient, at a ratio of about 1:1 to about 1:2 by volume. The bone marrow is permitted to soak into the scaffolding provided by the sponge, and the sponge is then kneaded by hand, thereby obtaining a pliable putty consistency that may subsequently be gently packed into the target site. The collagen in the sponge provides a malleable putty, non-water soluble carrier that permits accurate placement and retention of biological factors at the implantation site. However, if the surgeon over-manipulates the putty, or if there are excessive amounts of blood at the target site, the putty may lose some of its cohesiveness, which may cause some of the implant to flow out of the target site.
Accordingly, there is a need for improved bone void fillers suitable for repair of bone defects.